Rule 1: 1. The perfect: رَمَى، دَعَا، نَسِيَ
In the 3rd person masculine singular the original رَمَيَ and دَعَوَ contract to ramā and daʿā. The spelling preserves the lost radical: a verb in ي is written with alif maqṣūra, رَمَى, a verb in و with a plain alif, دَعَا. In the فَعِلَ type the ي follows a kasra and is stable: نَسِيَ, بَقِيَ, رَضِيَ. Before a suffix that begins with a consonant (ـتُ، ـتَ، ـتِ، ـنَا، ـتُمْ، ـتُنَّ، ـنَ) the radical reappears in its true shape: رَمَيْتُ, دَعَوْتُ, نَسِيتُ (for nasiytu: iy before a consonant is written and pronounced ī).
دَعَا الْإِمَامُ لِلْمُسْلِمِينَ بَعْدَ الصَّلَاةِ.
daʿa l-imāmu li-l-muslimīna baʿda ṣ-ṣalāti
The imam prayed for the Muslims after the prayer.
دَعَا for دَعَوَ: the و shows in the alif.
بَكَى الرَّجُلُ عِنْدَ سَمَاعِ الْقُرْآنِ.
baka r-rajulu ʿinda samāʿi l-qurʾāni
The man wept on hearing the Quran.
بَكَى for بَكَيَ: alif maqṣūra points to the ي.
رَضِيَ اللّٰهُ عَنِ الصَّحَابَةِ كُلِّهِمْ.
raḍiya llāhu ʿani ṣ-ṣaḥābati kullihim
God was pleased with all the Companions.
فَعِلَ type: the ي keeps its fatḥa after the kasra.
تَلَوْتُ سُورَةَ الْكَهْفِ يَوْمَ الْجُمُعَةِ.
talawtu sūrata l-kahfi yawma l-jumuʿati
I recited Sūrat al-Kahf on Friday.
تَلَا، يَتْلُو: before ـتُ the و comes back.
بَنَيْنَا مَسْجِدًا صَغِيرًا فِي الْقَرْيَةِ.
banaynā masjidan ṣaghīran fi l-qaryati
We built a small mosque in the village.
بَنَى، يَبْنِي: before ـنَا the ي comes back.
نَسِيتُ الدُّعَاءَ فَذَكَّرَنِي أَخِي بِهِ.
nasītu d-duʿāʾa fa-dhakkaranī akhī bihi
I forgot the supplication, so my brother reminded me of it.
نَسِيتُ: kasra + ي before a consonant gives ī.